1) Combinations of insulin and glucagon will be used to modify the rate of hepatic atrophy that occurs after a portal systemic shunt. 2) Auxiliary transplantation of the rat liver will be carried out with variations of the portal inflow and hepatic venous outflow so that the relationships between hepatic regeneration and hepatic competition can be clarified. 3) Amino acid mixtures administered either directly to the liver via a portal vein catheter or to the whole animal will be used in animals with defined insulin/glucagon ratios in a search for the hepatic stimulatory aspects of initiating factors of hepatic regeneration.